Private Brain Key Generation and Public Address Not Matching Java

I am trying to generate a public and private key set from a input string in Java. (Yes I am aware this can be a dangerous practice) I am using bitcoinj for a outside library.

I currently have:

 //public key generation from private key
 static String getPublicKey(byte[] privKey) {

    Address address = new Address(MainNetParams.get(), 
        Utils.sha256hash160(ECKey.fromPrivate(privKey, false).getPubKey()));

    return address.toString();

  }

 ///hash string to generate private key from string
 static byte[] sha256(String base) {
      try{
          MessageDigest digest = MessageDigest.getInstance("SHA-256");
          byte[] hash = digest.digest(base.getBytes("UTF-8"));
        return hash;
      } catch(Exception ex){
      throw new RuntimeException(ex);
      }
    }

 //encode private key as string to display
 static String privToString(byte[] hash) {

      StringBuffer hexString = new StringBuffer();

      for (int i = 0; i < hash.length; i++) {
          String hex = Integer.toHexString(0xff & hash[i]);
          if(hex.length() == 1) hexString.append('0');
          hexString.append(hex);
      }

      return hexString.toString();

  }

When I run the following: Seed String: icecreampaintjob

I get the following:

Public: 1KdoiXMYFn2qa8uGGiNqfrwFRDu3j2qQNA

Private: dba1e3e22415c56af772dee422add21b7382ea35f2af77852a8069d02e47ecf4

Using bitaddress.org to cross verify I get:

Private: 5KV1o7tRK8pNqrPNYyi38nrik9r2Y85sjdgFDttnDiT1uZrQ1fj (DOESN'T MACTH)

Public: 1KdoiXMYFn2qa8uGGiNqfrwFRDu3j2qQNA (MATCHES)

What am I missing?

John Down

Posted 2016-04-24T01:04:12.030

Reputation: 31

Answers

As bitaddress.org BrainWallet says in its display

Private Key (Wallet Import Format): 
5KV1o7tRK8pNqrPNYyi38nrik9r2Y85sjdgFDttnDiT1uZrQ1fj

Wallet Import Format is the usual base58 armoring applied to the privatekey value with 'version' 0x80.
See https://en.bitcoin.it/wiki/Wallet_import_format or in more detail https://en.bitcoin.it/wiki/Base58Check_encoding . This is basically a duplicate of Is there a way to generate a brain wallet from the command line or console? although that uses bash+dc rather than Java.

Not tested, but it looks to me like VersionChecksummedBytes(0x80,bytes).toBase58() does this.

dave_thompson_085

Posted 2016-04-24T01:04:12.030

Reputation: 244

Where is VersionChecksummedBytes? Is the method part of the bitcoinj library? – John Down – 2016-04-24T05:45:48.830

@JohnDown yes it's in bitcoinj. It's a class (in Java by convention class names start with uppercase letter and method names start with lowercase letter) and is the superclass of the Address class your code already uses -- that's how I found it. – dave_thompson_085 – 2016-04-25T03:12:43.433

Can you further explain? The method is protected and I can't access it from my main class. Right now I have: Address output = new VersionChecksummedBytes(0x80,privateKeyByte).toBase58(); – John Down – 2016-04-25T16:58:24.150

See Java docs: https://bitcoinj.github.io/javadoc/0.12.3/index.html?overview-summary.html

– John Down – 2016-04-25T21:11:30.390

In the code (where I looked) actually the ctor is protected (and I didn't notice) but the method is public. (1) It's opensource so you could change it. (2) It's Java so you could override with reflection. (3) But the cleanest way is just make a very simple subclass, and use that. And (4) when you do, the result from toBase58 (or toString which just wraps it) is String. – dave_thompson_085 – 2016-04-26T09:32:40.737

I think new VersionedChecksummedBytes(0x80, priv).toBase58() is the right idea, but the constructors are protected and I cannot find a static factory function. However, using the getPrivateKeyEncoded method of ECKey, we can obtain a DumpedPrivateKey object which derives from VersionedChecksummedBytes. We can also use the getPrivateKeyAsWiF method of ECKey which is more direct. Or we can do things manually:

import java.math.BigInteger;
import org.bitcoinj.core.VersionedChecksummedBytes;
import org.bitcoinj.core.ECKey;
import org.bitcoinj.core.NetworkParameters;
import org.bitcoinj.core.Sha256Hash;
import org.bitcoinj.core.Base58;
import org.bitcoinj.params.MainNetParams;



public class Test {
  public static void main(String args[]){

  NetworkParameters mainNet = MainNetParams.get();
  String hex = "dba1e3e22415c56af772dee422add21b7382ea35f2af77852a8069d02e47ecf4";
  BigInteger big = new BigInteger(hex, 16); 
  ECKey key = ECKey.fromPrivate(big, false);  // uncompressed
  byte[] priv = key.getPrivKeyBytes();

  String wif1 = key.getPrivateKeyEncoded(mainNet).toBase58();
  System.out.println(wif1); // 5KV1o7tRK8pNqrPNYyi38nrik9r2Y85sjdgFDttnDiT1uZrQ1fj

  String wif2 = key.getPrivateKeyAsWiF(mainNet);
  System.out.println(wif2); // 5KV1o7tRK8pNqrPNYyi38nrik9r2Y85sjdgFDttnDiT1uZrQ1fj

  byte[] bytes = new byte[1 + 32 + 4];
  bytes[0] = (byte) 0x80;
  System.arraycopy(priv, 0, bytes, 1, 32);
  byte[] checksum = Sha256Hash.hashTwice(bytes, 0, 33);
  System.arraycopy(checksum, 0, bytes, 33, 4);
  String wif3 = Base58.encode(bytes);
  System.out.println(wif3); // 5KV1o7tRK8pNqrPNYyi38nrik9r2Y85sjdgFDttnDiT1uZrQ1fj

  }
}

Beware that if you intend to do the same manual calculation for a compressed key, you need to add an additional byte 0x01 after the 32 bytes secret and just before the checksum. If you want to do the same thing for a testing network, replace the front version byte 0x80 by 0xef.

Sven Williamson

Posted 2016-04-24T01:04:12.030

Reputation: 1 314